In recent years, research and development of display devices typified by flat panel displays have been actively pursued, and transistor used in many of them are formed over a glass substrate and use silicon semiconductors such as amorphous silicon and polycrystalline silicon.
In view of this, attention has been drawn to a technique by which a transistor is manufactured using an oxide semiconductor instead of using a silicon semiconductor, and applying this transistor to electronic devices and optical devices. For example, Patent Document 1 and Patent Document 2 disclose techniques by which a transistor is manufactured using zinc oxide which is a single-component metal oxide or an In—Ga—Zn—O-based oxide which is a homologous compound as an oxide semiconductor, and is used as a switching element or the like of a pixel of a display device.
Also, many of the transistors using an oxide semiconductor use an amorphous oxide semiconductor for a channel region. With a transistor using an amorphous oxide semiconductor, higher field effect mobility can be obtained compared to a transistor using amorphous silicon. However, for application to a high performance device, an oxide semiconductor with high crystallinity with which even higher field effect mobility can be obtained is desired, and research and development of various crystallization techniques is underway (see Patent Document 3 and Patent Document 4).